Hitherto, turbofans including three-dimensionally shaped fan blades have been widely employed as air-sending fans included in indoor units of ceiling-concealed air-conditioning apparatuses. Specifically, a turbofan is configured to take in air from a portion thereof on the inner circumferential side and to blow out the air toward the outer circumferential side thereof and includes a disc-shaped main plate, a ring-shaped shroud facing the main plate, and a plurality of blades (wings) each having two ends thereof connected to the main plate and the shroud, respectively. Several inventions have been disclosed in response to demands for more silent operation (noise reduction).
For example, there is a technology in which a rear edge portion of each blade extending in the width direction of the blade has a “saw-tooth shape” defined by a line angled alternately toward two sides in the longitudinal direction of the blade, (see Patent Literature 1, for example).
In another technology, each blade has, on a rear edge portion of a front surface (positive-pressure surface) thereof in the direction of rotation, a plurality of “ribs” provided parallel to one another at predetermined intervals and extending in a direction perpendicular to a rotating shaft (see Patent Literature 2, for example).
In yet another technology, each blade has “riblets” provided over the entirety or a portion of the pressure-receiving-surface side thereof on a rotating shaft of the impeller (see Patent Literature 3, for example).